Transcript for 'American Sniper' Allegedly Gunned Down by Fellow Veteran

unfolding tragedy a former navy s.E.A.L., A hero to members of the military. This evening authorities say he was targeted and killed by a fellow veteran. That s.E.A.L., Chris kyle, took out more u.S. Enemies than anyone else ever did as a sniper. He often said he preferred to think about the lives he saved doing it. After four tours in iraq, he returned to help american troops recrom the invisible wounds of war. Tonight this young man, eddie routh, is accused of killing him. Abc's ryan owens is in texas and he leads us off tonight. Reporter: Former navy s.E.A.L. Sniper chris kyle was such a good shot he once hit a target more than a mile away, but police say it was a bullet fired at point blank range that ended the life of the husband and father of two. I'm a better husband and father than I was a killer. Reporter: The 38-year-old died at a place he should have felt comfortable, this gun range southwest of dallas. And detectives say he died at the hands of a young man he was trying to counsel. The suspect's mother, she may have reached out to mr. Kyle to try and help her son, and we kind of have an idea that maybe that's why they were at the range for some type of therapy. Reporter: Officers arrested this 25-year-old former marine, eddie ray routh, after a police chase saturday night. They say routh turned the gun on kyle and a friend, 35-year-old chad littlefield, murdering them both. His family told them he was having trouble readjusting to life at home after years of war. That's something kyle spoke about frequently. You don't have an identity. You have to learn a whole new way to act. Reporter: Kyle volunteered to help vets suffering from post-traumatic stress disorder. He knew the stress of combat as well as anyone. He served four deployments, won seven medals of bravery and killed more than 150 people. He was the deadliest sniper in u.S. Military history. I loved the job, you know, the guy, the camaraderie. It came down to where I had to choose them or my wife and kids. I couldn't have both anymore because I'd already messed that up. So I chose the family. Reporter: On the home front kyle became a best selling author. In his autobiography "american sniper" he writes of shooting so many iraqi insurgents they nicknamed him the devil and placed a $20,000 bounty on his head. To survive all of that only to be killed here at home. Tonight that young marine faces two counts of capital murder, one for each of the men who was trying to help him heal. David?

This transcript has been automatically generated and may not be 100% accurate.